Though the “K-On!” movie is yet to open in the future on Dec. 3, J-Cast observed that on movie tickets completely sold out on April 29. Why had the sales spiked so much prior to the movie's release? It turns out that ardent fans were desperate to get their hands on limited-edition merchandise.

Movie goers who order a ticket to see “K-On!” in advance get the perk of a clear plastic file that depicts a character from the anime drama. There are five files to collect and fans have been buying up to five tickets together in order to collect each one. Some fans even camped over night to get their mitts on these desirable slivers of brightly colored plastic. Stocks are now running low and a cinema in Kumamoto, for instance, reports that it has run out of the special files.

"K-On!" merchandise has been insanely popular. Back in November last year we reported on Lawson’s "K-On!" campaign. The convenience store sold specially branded K-On! snacks as part of a special campaign, some of which were so popular that they immediately sold out. This caused a huge commotion on the net among disgruntled "K-On!" fans who pride themselves on owning complete collections of all "K-On!" merch.

If you haven’t heard of "K-On!" before, here's the takeaway: It’s a gentle, light comedy, bursting with saccharine sweet cuteness. Debuting in April 2009 on TBS, it follows the fortunes of five cute high school girls who decide to start a music club and a rock band is born.

The runaway success of the K-On! movie campaign is sure to inspire marketers to get busy to create similar limited-edition items.